Drs. Vikas Malhotra, Mary Li and Thomas Huayang Tang received a total of more than $20 million from the federal health program for seniors and the disabled, according to data released Wednesday.

All are oncologists, a medical specialty that dominates the list of the most highly reimbursed Medicare providers, in large part because of the expensive drugs they use.

According to the data, in a single year, Malhotra, a specialist in blood-related cancers, billed Medicare for services provided to 1,783 patients in 2012. He was reimbursed $8.4 million.

Drs. Li and Tang were reimbursed $6.1 million and $5.8 million, respectively, in 2012.

Malhotra, a former University of Missouri professor who has been practicing in Florida since 2003, stressed that most of the money his office gets from Medicare goes right back out the door to pay for drugs, lab tests and other expenses. Payments to oncologists typically include the cost of medications, which are purchased by the practice.

"That doesn't represent the income of the physician," he said.

The data release is the biggest public disclosure in Medicare's 50-year history, and comes at the urging of employers, insurers, consumer groups and media outlets eager to open the books on health care finance. It includes only payments to doctors, not those made to hospitals, which were disclosed last year. It also does not include Medicare Advantage managed care plans, which cover about a third of Florida Medicare beneficiaries and are run by private insurers that reimburse doctors.

Jonathan Blum, principal deputy administrator for the U.S. Centers for Medicare & Medicaid Services, told reporters Wednesday that oncologist and ophthalmologist payments tend to be higher because of drugs. Medicare pays doctors the average market price of the drug, plus 6 percent of the price to administer the medications, he said.

By law, Blum said, Medicare can't tell a doctor to substitute a cheaper drug, even if less expensive medications are proven just as effective. But officials hope a public spotlight could cause doctors to consider less expensive alternatives. "While we are limited by statute … we can certainly inform the public," he said.

Dr. Bill Harwin, founder of Florida Cancer Specialists, which is based in Fort Myers and has about 80 offices statewide, said it's not surprising his company's doctors in Hernando County should have such high Medicare reimbursements.

"That's a particularly busy area that's underserved," he said.

Malhotra, 45, said he and his two colleagues saw their practice explode during 2012 after several oncologists in the area either retired or left the county.

"We each see 30 to 40 patients a day and each of our nurse practitioners sees another 15 to 20," said Malhotra, who is paid a salary plus bonus by Florida Cancer Specialists. "We are all super producers, but not by choice."

Malhotra said the practice has never been the subject of anything other than routine Medicare audits.

Dr. Adam Rosen, a Clearwater rheumatologist, received $4 million in Medicare reimbursements in 2012. But he pointed out that his entire practice — three doctors and one nurse — bill Medicare under his name.

He emphasized that the payments to his practice also include the price of expensive medications — on average, about $5,000 per infusion — and that reimbursements don't always cover actual expenses.

"It's really a meaningless number all by itself," he said.

Federal officials said making payment information public could help root out fraud and waste in the Medicare program. By studying payments at the individual doctor level, for instance, researchers could better understand why Medicare spending varies so much by geography.

"These are questions the agency can't answer by itself," Blum said. "We believe as a policy matter that this data needs to be made public."

But they also cautioned that the information — which says nothing about quality of care — has limits. Blum noted, for instance, that well-known specialists draw a lot of patients, and that could legitimately mean high numbers.

The American Medical Association and other physician groups objected to the data release, saying it could be full of inaccuracies and ambiguities.

Perched atop the state and national lists is West Palm Beach ophthalmologist Salomon Melgen, paid $20.8 million in 2012. He is under criminal investigation for alleged excessive billing.

Out of more than 825,000 physicians in Medicare's claims data base, just 344 physicians received at least $3 million apiece for a total of nearly $1.5 billion.

The Health and Human Services inspector general in an audit last year recommended Medicare automatically scrutinize total billings above $3 million, but Medicare officials on Wednesday declined to identify what would trigger an audit.

About 1 in 4 of the top-paid doctors — 87 of them — practice in Florida. California had 38 doctors in the top group, New Jersey had 27, Texas had 23, and New York had 18.

Nationwide, in the $3 million-plus club, 151 ophthalmologists accounted for nearly $658 million in Medicare payments, leading other disciplines. Cancer doctors rounded out the top four specialty groups, accounting for a combined total of more than $477 million in payments.

The same pattern held in Florida, where nearly 300 radiation oncologists received a total of $243 million, or an average payment of $820,000. Just over 1,100 opthalmologists got nearly $568 million, for an average payment of nearly $515,000.

Rheumatology, dermatology and cardiology were also among top-paying specialties, with average payments of $435,000, $428,000 and $354,000, respectively, in Florida.

The high number of ophthalmologists in the top tier may reflect the doctors' choice of medications. Studies have shown that Lucentis, a pricey drug for macular degeneration, works no better than a much cheaper one, Avastin. But lower-cost Avastin must be specially prepared for use in the eye, and problems with sterility have led many doctors to stick with Lucentis.